New monazite U-Pb age constraints on the evolution of the Paleoproterozoic Vaasa granitoid batholith, western Finland

作者：Kotilainen Anna K^*; Manttari Irmeli; Kurhila Matti; Holtta Pentti; Ramo O Tapani

来源：Bulletin of the Geological Society of Finland, 2016, 88(1): 5-20.

DOI：10.17741/bgsf/88.1.001

• monazite
• U-Pb geochronology
• anatexis
• granitoid
• Svecofennian
• Vaasa
• Finland

The Vaasa batholith, western Finland, is a large, peraluminous granitoid pluton that crystallized at 1.88-1.87 Ga during the culmination of the Svecofennian orogeny. The batholith has gradual contacts, through metatexites and diatexites, with the enveloping metasedimentary rocks of the Bothnian Belt. We present ID-TIMS U-Pb age data on monazite from granitoids and xenoliths of the Vaasa batholith and combine these with published U-Pb zircon ages in order to shed further light on the evolution of the Vaasa batholith. The apparent monazite ages for seven of the examined samples are 1870-1863 Ma, and 1855+/-3 Ma for one further sample from the southern part of the batholith. Combined with pre-existing data, the monazite ages of the granitoids are 9 to 18 Ma (face values) or 3 to 9 Ma (external errors considered) younger than the U-Pb zircon crystallization ages from respective samples. Our new data suggest slow cooling for the Vaasa batholith - the closure/saturation temperature of the monazite U-Pb system was probably reached in similar to 10 m.y. after the crystallization of magmatic zircon in the examined rocks.

• 出版日期2016